Properties of Passivation Film

The thickness of the passivation film generally ranges from 0.5 to 1 micrometer (μ). It is highly stable, with a dense structure and a transparent metallic appearance. The passivation film seals the pores of the galvanized layer, preventing the anodic dissolution of zinc, thereby extending the service life of galvanized steel pipes and enhancing their corrosion resistance. The hexavalent chromium in the passivation film also plays a role in repairing damaged films. The color of a thick passivation film shifts from red to yellow as the hexavalent chromium content decreases. Thin passivation films exhibit iridescent colors due to light interference. Within 24 hours of formation, the corrosion resistance, adhesion, and hardness of the passivation film are relatively weak. When the passivation film is dried at temperatures above 70°C, its corrosion resistance is poor.